Ambidentate Ligand Research Articles

Preparation and Properties of Cobalt(III)–1,2-Bis(dimethylphosphino)ethane (dmpe) Complexes of the [Co(L)(dmpe)2]n+ Type

Abstract Seven new cobalt(III)–phosphine complexes of the type [Co(L)(dmpe)2]n+ were prepared from trans-[Co(Cl or Br)2(dmpe)2]+, where dmpe denotes (CH3)2PCH2CH2P(CH3)2, and L is C2O42−, NH2CH2COO−(gly), NH2CH(CH3)COO−(ala), (C2H5)2NCS2−(dtc), (NCS−)2, (NCO−)2, or (CN−)2. Reactions of cis-[CoCl2(dmpe)2]+ with X− (X−=CN−, NCS−, and NCO−) yielded only trans-[CoX2(dmpe)2]+. Qualitative stabilities of the complexes containing a bidentate ligand in aqueous solution were found to decrease in the order L=CH(CH3CO)2−(acac), C2O42−, dtc>CO32−>>gly, ala>NH2CH2CH2NH2(en); the complexes containing O or S donor atoms are thermally more stable than those containing an amino donor group. The d–d absorption bands of the complexes were assigned by comparing the spectra with those of related Co(III)–phosphine and -en complexes. The IR and visible absorption spectra of the NCS− and NCO− complexes indicate an N coordination mode of these ambidentate ligands.

Sulphur–arsenic ligands. Dimethyl(methylthio)arsine complexes of halogenotrimethylplatinum(IV) and tricarbonylhalogenorhenium(I)

Dimethyl(methylthio)arsine, AsMe2(SMe)(L), is a potentially ambidentate ligand with the possibility of arsine and/or sulphur co-ordination to a transition metal. We have investigated the reaction of the ligand for the scission of the tetrameric trimethylplatinum halides, and that for carbon monoxide displacement from the rhenium pentacarbonyl halides. In both of these reactions organic arsines and sulphides individually are known to be effective, producing well characterised stable products. Ligand L reacts with [(PtXMe3)4](X = Cl, Br, or I) and with [ReX(CO)5](X = Cl, Br, or I) to yield respectively fac-[PtXMe3L2] and fac-[ReX(CO)3L2] in good yield. Hydrogen-1 and 13C n.m.r. studies demonstrate that in all complexes the ligand behaves in a monodentate manner with exclusively arsenic–metal bonds. In solution the compounds give no indications of any fluxional behaviour in the temperature range –80 to +80°C. The fac structure of all of these complexes gives rise to the interesting observation that all three methyl groups in the co-ordinated ligand AsMe2(SMe) are non-equivalent.

ChemInform Abstract: Unusually Detailed Insight into the Dynamic Behavior of Coordinated Ambidentate Ligands.

AbstractEndocyclic N‐bound 2‐aminopyridine when coordinated to B12 coenzyme models simulates the very long Co‐ N bonds characteristic of axially bound 5,6‐dimethylbenzimidazole in cobalamins.

ChemInform Abstract: New Polyphosphorus Ligands: Addition Reactions of 1,1‐Bisdiphenylphosphinoethene.

AbstractAs outlined in the scheme, 1,1‐bis(diphenylphosphino)ethene (I) reacts with P‐ and As‐compounds, such as (II), (IV) or (XI), to yield adducts such as (III), (VI) or (XIII), which can be converted into complexes, e.g. (XVI).

Unusually detailed insight into the dynamic behavior of coordinated ambidentate ligands. Factors influencing the binding mode of 2-aminopyridines in B12 models

Unusually detailed insight into the dynamic behavior of coordinated ambidentate ligands. Factors influencing the binding mode of 2-aminopyridines in B12 models

Alkenylphosphane RPX 2 und R 2PX (X = NEt 2, CI): IHRE funktion als einzähnige liganden und potentiell hemilabile chelatbildner in metall(0)-komplexen

Depending on reaction conditions various types of substitution products are obtained from (CO) 6M (M = Cr, Mo, W) and the ambidentate ligands L = RPX 2 and R 2PX (R = vinyl, allyl, 2-vinylphenyl, 2-allylphenyl; X = NEt 2, Cl, Br): (CO) 5ML, (CO) 4ML 2 or chelate compounds (CO) 4ML, in which L is coordinated via P and the olefinic bond. Reactions of coordinated ligands, leading to (CO) 5CrRPNEt 2Br and (CO) 5CrRPH 2 (R = 2-vinylphenyl) are reported. In some cases L (R = 2-Vinylphenyl; X = NEt 2) proves to be hemilabile on reaction of the complex (CO) 4CrL with Lewis bases. Thus, e.g. with CO at room temperature and normal pressure (CO) 5ML iwth P-bonded L is formed, from which the educts can be recovered by gentle warming. The NMR spectra ( 1H, 13C, 31P) of the compounds are discussed.

New polyphosphorus ligands: addition reactions of 1,1-bisdiphenylphosphinoethene

The reactivity of the double bond adjacent to the geminal diphenylphosphino groups of (Ph2P)2CCH2 facilitates the addition of species with one or more P–H bonds to provide a convenient high-yielding route to a range of new poly- and ambi-dentate ligands which can form a wide variety of different types of transition metal complex.

Complexes of 5,7-dimethyl-1,8-naphthyridine-2-ol(dimenol): EPR spectra of an unusual copper(II) dimer containing dimenol and acetate bridges, and crystal structure of [Rh(O 2CC 3H 7) 2(dimenol)] 2

The preparations are reported of complexes of 5,7-dimethyl-1,8-naphthyridine-2-ol (= dimenol) with metal ions of the series MnZn. Reaction of dimenol with copper(II) acetate yields a dark blue complex of stoichiometry Cu(dimenol)(CH 3CO 2) which, from its X- and Q-band EPR spectra, is dimeric containing antiferromagnetically coupled pairs of Cu(II) ions. Analogous reactions with rhodium(II) acetate and butyrate gave the adducts [Rh(O 2CR) 2(dimenol)] 2. The intense violet butyrate [Rh(O 2CC 33H 7) 2(dimenol)] 2 crystallizes in the space group P2 1/ n with a = 11.474(2), b = 10.247(1), c = 17.129(3) Å, β = 101.67(1)°, and Z = 2. It has the standard dinuclear rhodium(II) carboxylate lantern structure with RhRh = 2.409(1) Å. The dimenol ligands coordinate in axial positions via N(8) of the naphthyridine The RhN distance (2.387(4) Å) is one of the longest yet reported. Attention is drawn to a potential danger in using colour as an indicator of coordination mode of an ambidentate ligand L in [Rh(O 2CR) 2L] 2 complexes.

Syntheses with η 5-C 5H 5V(CO) 3THF: Generation, and substitution reactions. First observation of 51V- 117,119Sn coupling

The complex CpV(CO) 3THF has been prepared in THF solution (i) photochemically from CpV(CO) 4, and (ii) from [CpV(H)(CO) 3] −/[Ph 3C] + at low temperatures. THF is replaced by [CpV(H)(CO) 3] − to form [{CpV(CO) 3} 2-μ-H] −, and by various ligands L with C, η 2-CC, Sn, N, O, S, Se or Te functionality to yield CpV(CO) 3L and cis-[CpV(CO) 2LL] (LL = bipy, o-phen, tolane). The δ ( 51V) values range over ca. 1400 ppm and allow the assignment of distinct coordination modes for ambidentate ligands. The temperature gradient is ca. +1.2 ppm/deg. For [CpV(SnCl 3)(CO) 3] − (δ −1340 ppm rel. to VOCl 3), 1 J( 51V- 117,119Sn) is 900 Hz. The isotope effect on introducing 12CO for 13CO in CpV(CO) 4 is −0.48(2) ppm; 1 J( 51V- 13C) 107 Hz.

Phosphinsubstituierte chelatliganden: XI. NMR-spektroskopische untersuchungen ( 1H, 13C, 31P, 55Mn) an halogentricarbonylmangan-chelatkomplexen mit phosphino-thioformamid- und -thioformimidoester-liganden

A series of halotricarbonylmanganese chelate complexes, fac-(CO) 3Mn(X)L (X = Cl ( a), Br ( b), I ( c)), with thioformamide (L = Ph 2PC(S)NRMe; R = H ( 1), Me ( 2), Ph ( 3)) and the isomeric thioformimidoester (L = Ph 2PC(NR)SMe; R = Me ( 4), Ph ( 5)) ligands were prepared by thermal CO substitution of the pentacarbonylmanganese halides. The IR and NMR data indicate P,S-coordination of the ambidentate ligands and uniform Z configuration in 3–5. Due to the large linewidth of the NMR signals, the 4 J(PH) and 3 J(PC) coupling constants could not be determined for the thioamide complexes 1–3. Coordination of the thioimide 4 causes an increase in 4 J(PH) whereas 3 J(PC) remains unchanged. δ( 31P) shows a downfield coordination shift as usual for manganese complexes. The broad 55Mn NMR signals cover a range of +90 to −730 ppm (rel. KMnO 4) with the imidoester complexes 4 and 5 at the low-field side. The normal halogen dependence Cl < Br < I is observed for 55Mn shielding.

Formation of isomeric dimolybdenum(II) compounds using the potentially ambidentate ligands [R2PC(S)NR']- (R/R' = Ph/Ph, Ph/Me) and [Me2NC(S)NPh

Preparation et proprietes des 4 complexes de formule Mo 2 [R 2 XC(S)NR'] 4 avec R 2 X/R'=Ph 2 P/Ph, Ph 2 P/Me, et Me 2 N/Ph, determinees par diffraction RX et diverses mesures spectroscopiques

Complexes of 3,4-dihydroxyphenyl derivatives. VII. Mixed ligand complexes of L-dopa and related compounds

The stability constants of the mixed ligand complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) ions with L-dopa, dopamine, L-adrenaline and L-noradrenaline as ligand A and L-alanine, L-histidine, glycylglycine and ATP as ligand B were determined pH-metrically at 25 °C and an ionic strength of 0.2 mol/dm 3 (KCl). From visible spectral studies, conclusions were drawn on the bonding properties of the ambidentate ligands in the complexes. It was found that, even in its mixed ligand complexes, the ambidentate nature of dopa permits its coordination via the amino acid side-chain (N, O) at lower pH, and via the ortho phenolic hydroxy groups (O, O) at higher pH. At the same time, the complex-forming tendency of the ethanolamine side-chain in the catecholamines plays a minor role in the mixed ligand complexes. The stabilities of the mixed ligand complexes were interpreted by consideration of the differences in the stepwise stability constants of the parent complexes, the back-coordination, the charge neutralization, and the electrostatic and hydrophobic interactions between the ligand pairs.

Spectral investigation of intermolecular interactions of formyl- and acylderivatives of azoles and pyridines with nitrophenols

Abstract Systematic investigation of H-complex-formation of ambidentate ligands - carbonyl derivatives of azoles and pyridines of varying basicity with mono-, di- and trinitrophenols has been fulfilled by IR- and UV-spectroscopy. Complex-formation proceeds exclusively via pyridine-type nitrogen atom and is followed by the polar bond formation of the N δ+ ⋯ H⋯O δ− type. Composition, equilibria constants and probable conformations of H-complexes in non-aqueous media have been determined.

Macromolecular nature of nucleic acids in metal interactions

The conformational changes of nucleic acid macromolecules as a result of rotation around CC, CO, CN covalent bonds occur without destruction of the chains, but they can lead to the loss of biological function; this can be seen in interactions with metal ions of nucleic acids. The latter are ambidentate ligands and supply by complex formation different sites of binding, sometimes cooperatively, in polyfunctional chains. This leads to the formation in nucleic acid macromolecules of different coordination centers, among them the unsaturated, deformed type: pure phosphate, mixed phosphate-base, pure base, crosslinked base, sandwich, complementary paired base and others. The probability of the centers is discussed. As a result of complex formation with nucleic acid macromolecules there are mutual influences between fuctional groups of the chain, those of electronic origin, conjugations, fields effects, dispersion interactions, hydrogen bonding, solvation, supermolecular structure formation and so on. The interactions mentioned can not so far be expressed in quantitative ways nor can their contributions to equilibrium constants of macromolecular complex formation be written explicitly, therefore the way of describing polymeric complexing systems is through the use of averaged values. Various examples of the interactions of metal ions with macromolecular chains of DNA and RNA, pH-dependence, conformational changeability and reversibility, as well as the possibility of modelling the macromolecules under study are given.

Coordination chemistry of methylmercury(II). Synthesis, hydrogen-1 NMR, and crystallographic studies of cationic complexes of MeHg(II) with ambidentate and polydentate ligands containing pyridyl and N-substituted imidazolyl donors and involving unusual coordination geometries

Complexes [MeHgL]N03 (L = 4,4’,4’’-triethyL2,2':6’,2”-terpyridyl (Et3terpy), terpy, bis(2-pyridy1)methanes ((py)CH2's), (py)2CMe2, (py)2CEt2, tris(2-pyridyl)methane, several N-alkylimidazoles, N-(2-pyridyl)imidazole, and N-methyl-2-(2-pyridy1)imidazoles) are obtained from addition reactions in acetone. Proton magnetic resonance spectroscopy is used to deduce coordination behavior of potential uni- or polydentate ligands in methanol, indicating that Et3terpy, terpy, (py)2CH2's, and N-methyl-2-(2-pyridyl)imidazoles act as bidentates to give three-coordinate mercury, but (py)2CR2 (R = Me, Et) are present as unidentates. A linear relation is obtained between 2J(1H-199Hg) for [MeHgL]+ and protonation constants for L, where L = N-alkylimidazoles, and the relation is similar to that obtained previously for L = pyridines. The ambidentate ligand N-(2-pyridyl)imidazole binds to mercury via the imidazole ring. Crystalline [MeHg((py)2CH2)]N03 has (py)CH2 present as a bidentate ligand with “T-shape” coordination geometry based on a dominant C-Hg-N moiety [Hg-N = 2.16(1) A, C-Hg-N = 172 (1) and a weaker Hg-N’ bond [2.75(2) A]. Crystalline [MeHg(Et3terpy)]N03 has Et3terpy present as a tridentate ligand with MeHg(II) bonded strongly to the central nitrogen [2.26(2) A, C-Hg-N = 171(1) and weakly to the terminal nitrogens [2.51(2), 2.61(2) A]. Syntheses of new ligands containing pyridyl and N-methylimidazolyl donor groups are described.

Structure of isothiocyanate methemoglobin

The structure of the complex of the ambidentate ligand thiocyanate with horse methemoglobin was compared with that of acid methemoglobin and azide methemoglobin by X-ray difference Fourier techniques. Thiocyanate is co-ordinated to iron exclusively by its nitrogen atom, and thus forms the isothiocyanate complex. The ligand is bent as in the stereochemically very similar azide complex, and there is no evidence for strain in the ligand pocket of the globin, in contrast to earlier results on the cyanide complex. The higher spin of the isothiocyanate complex compared with azide is accompanied by only slight structural changes at the hemes, the most prominent of which is interpreted to be a slight lengthening of the iron—ligand nitrogen bond in the β-heme.

Electronic, counterion and medium effects on the bonding mode of the seleno-cyanate ion in trans-hydridoselenocyanatotetrakispiperidineiriduium(III) complexes

The results of infrared spectral studies of the complexes trans-[Ir(pip) 4(H)CNSe]Y (pip = piperidine; CNSe − = selenocyanate ion, bonding mode unspecified; Y = NCSe −, B(C 6H 5) − 4, and ClO − 4), both in the solid state and in solution, having shown them to be ideal systems for the investigation of ambidentate ligand bonding mode controls. The greater stability of the N-bound selenocyanate, with SeCN − as the counterion, both in the solid state and in solution (irrespective of solvent dielectric), serves to further confirm the existence of antisymbiosis in an octahedral complex of a class (b) metal involving a strong trans-director (H −) with no π-bonding capability. The greater stability of the Se-bound selenocyanate, with B(C 6H 5) − 4 as the counterion, in the solid state is a clear-cut example of counterion bonding mode control. The selenocyanato—tetraphenylborate complex was found to be subject to a KBr-assisted isomerization in the solid state, and all three complexes were observed to undergo a heterogeneous KBr-catalyzed ionization of the coordinated SeCN − ion in DMSO solution, when studied in KBr cells. In CH 2Cl 2 solution, where minimal KBr catalysis is observed, hydride transfer to the solvent, with a concomitant loss of NCSe − to give a five-coordinate intermediate, which recombines with NCSe − to form trans-[Ir(pip) 4(SeCN) 2] +, occurs instead over an extended time period. The vCN frequency frequency of the non-coordinated NCSe − is very sensitive to the solvent dielectric, suggesting the existence of H-bonding to the amine proton of the piperidine ligands in the low dielectric solvents. The complexes trans-[Ir(pip) 4(H)X] ClO 4 (X = NCS −, CN −) were included in the study, for purposes of comparison. The vIrH frequency exhibited by the cyanide complex was found to be very low, due to the strong trans-influence of the cyanide group.

Metal complexes of sulfur–nitrogen chelating agents. V. 2-N-Ethylaminocyclopentene-1-dithiocarboxylic acid complexes of Ni(II), Pd(II), Pt(II), Co(II), Co(III), and Cu(I)

2-N-Ethylaminocyclopentene-1-dithiocarboxylic acid (EACDA) acts as an ambidentate ligand toward several metal ions. Bis-chelates have been obtained with Ni(II), Pd(II), Pt(II), and Co(II), and tris-chelate with Co(III). Cu(I) forms a 1:1 complex. The bonding sites involved in the metal chelates and their stereochemistry have been ascertained from electronic, infrared and nmr spectra, magnetic moment, and thermal analysis. In the Co(II) and Co(III) chelates bonding takes place from (S,S−) donor sites, whereas in the Ni(II), Pd(II), and Pt(II) chelates (N,S−) type bonding occurs. The Cu(I) complex appears to be polymeric in nature.

Symbiosis versus antisymbiosis: a study of the thiocynate bonding mode in trans-hydridothiocyanatotetrakispiperidineiridium(III) thiocyanate and tetraphenylborate

Examples of symbiotic and antisymbiotic behavior involving ambidentate ligands such as the NCS − ion have thus far been restricted to, respectively, octahedral complexes of class ‘a’ metals and square planar complexes of class ‘b’ metals. In the latter case, only the strong trans-influence of π-acid ligands heretofore been observed to cause antisymbiosis. The title complex was chosen for study because it involves an octahedral complex of an ambidentate ligand and class ‘b’ metal (re: [lr(SCN) 6] 3−) wherein the former is subjected to the strong trans-influence of a ligand which can only function as a σ-base. In the solid state, antisymbiosis is demostrated by the stability of the N-bound trans-[lr(pip) 4H(NCS)]NCS, and counteranion control by the synthesis and stability of the S-bound isomer as the BPh 4 − salt. When trans-[lr(pip) 4(NCS)(H)]NCS or its BPh 4 − salt as put into solution, IR studies indicate that N-bonding initially prevails in solution, irrespective of solvent dielectric. The prolonged aging of methylene chloride solutions of either trans-[lr(pip) 4(NCS)(H)]NCS or of trans-(pip) 4(SCN)(H) BPh 4 produces the soluble cation trans-[lr(pip) 4(SCN) 2] +. The νCN frequency of the noncoordinated NCS − is remarkably sensitive to the solvent dielectric, suggesting the existence of H-bonding to the amine proton of the piperidine ligands in the low dielectric solvents. NMR data support the existence of the mixture of six- and seven-coordinate species in all solvents forthe NCS − salt, as a consequence of the observation for each solution of a doublet hydride resonance. Solutions of the BPh 4 − salt, on the other hand, exhibit only a single hydride resonance, indicating the presence of the only a six-coordinate moiety.

Complexes of thiazoles. Part IV. Acetamido-thiazoles as ambidentate ligands

Some complexes of 2-acetamidothiazole and 2-acetamidobenzothiazole with NiII and CuII have been prepared and three types of co-ordination behaviour distinguished on the basis of their i.r. spectra. The organic ligand donor atoms may be (a) carbonyl oxygen and thiazole nitrogen, (b) amide nitrogen and thiazole nitrogen, or (c) carbonyl oxygen, amide nitrogen, and thiazole nitrogen. Types (b) and (c) are of interest as examples of co-ordination via a non-deprotonated amide nitrogen atom.